I base my work on principles of physics that are supported by laboratory measurements while relying on analytical mathematics to construct models. Making my own measurements is essential to grounding in reality. Some projects use a combination of tools. My interests are heat transfer, light, and gravitation because all are important to the behavior of large bodies.
Please see “Discoveries” for more information on previous work, which forms the basis of the current projects listed below.
The particular combination of modern instruments in the laboratory (see “Photos”) is unique, centering on how matter interacts with energy. “Photos” also contains pictures of collaborators and recent students.
Some like it Hot
Length-Scale Physics of Heat Transport
Values obtained for thermal diffusivity using our Laser-Flash apparatus (see “Photos”) depend on sample size. This technique removes spurious ballistic radiative transfer while avoiding unwanted contact losses. Length-scale dependence behavior is observed for metals (see figure and https://www.mdpi.com/1996-1944/14/2/449) as well as for insulators (Measurements, Mechanisms, and Models of Heat Transport) and indicates that heat-on-the-move is light, where the mechanism of transport is emission/re-absorption. Evidence also exists in the thermal diffusivity increasing with temperature above ~1000 K (Hofmeister, , Dong, and Branlund 2014, Journal of Applied Physics; http://dx.doi.org/10.1063/1.4873295).
The currently popular description of heat transfer is that pseudo-particles called phonons move energy across insulators. Although energy is stored in vibrations, this is heat content, not heat moving around.
Solids are explored in a 2022 paper by Hofmeister, Criss and Criss (https://doi.org/10.3390/ma15072638). We are working on a theory for gases now, and applying this to stars (see below).
Thermal expansivity, an underexplored physical property in Earth and Planetary science
Equations-of-state are constructed using the material properties of thermal expansivity (alpha = V-1dV/dT|P) and bulk modulus (BT, the inverse of beta = V-1dV/dP|T), where V = volume, P = pressure, and T = temperature. Direct (elasticity) measurements of bulk moduli have received much focus as accuracy is greater than X-ray diffractometry (XRD) of V vs. P. Similarly, alpha from XRD is an average over the T range explored. Hence, neither alpha at 298 K, nor its T dependence are well-known and extrapolations pose a problem. Because interferometry is not suited for grainy and darkly colored geological materials and relevant high T, dilatometry is the best currently available method for measuring alpha of such materials.
This project is in collaboration with Prof. Paul Giesting, who is an expert in crystallographic studies and a Washington U. alumnus. His current project concerns feldspars. My current project concerns glasses and rocks.
Some like it Cold
Using spectroscopy to identify star dust
Astronomical measurements of infrared spectra show signatures of dust superimposed upon stellar emissions. The ejected stardust is later incorporated in forming stars. To identify dust that exists in space, we collect IR reflectivity spectra and thin film data of material in meteorites, and best guesses of what is out there. Quantitative analyses of these data provide optical functions and emission spectra, which can be used to infer grain sizes, as well as chemistry and structure. Application of the data is made by collaborators in astronomy: currently, Dr. Janet Bowey (Cardiff Univ., UK). See, e.g., https://academic.oup.com/mnras/article/513/2/1774/6565807?login=true.
Collecting data at cold temperatures is the current project.
Wanted: Grad Student Help
A graduate student with mathematical skills (e.g., solving differential equations) and laboratory experience would best fit in with the projects being pursued.